Should We Sample More than Required by the European Water Framework Directive? Case study: Emscher Catchment

Abstract

Measurement of restoration success is a challenge, especially in multiple-stressed urban systems. Standard indicators for ecological assessment may be too robust to indicate small but continuous improvements. Thus, a standardized method of the European Water Framework Directive (EU WFD) is extended by additional samplings of macroinvertebrates in the urban Emscher catchment. The aim is to prove whether additional sampling adds value to interpretate restoration success. According to the EU WFD, the Emscher's ecological status and potential are mainly identified as good to moderate regarding biological components of macrophytes and macroinvertebrates, whereas bad regarding fish communities. The additional sampling improves the quality of the biological dataset, because twice as many species of macroinvertebrates are found compared to the WFD method. Hence, the additional sampling allows a stronger indication for community ordination, and community metrics describing diversity, dispersal, and feeding preferences as well as by disentangling the roles of environmental variables. Nevertheless, it is concluded that the standardized and simple WFD method is sufficient to capture the most relevant effects. However, if the budget is allowed and information on the species pool, nature conservation, or aspects of early indication are needed, it may be useful to implement an additional sampling of macroinvertebrates.